1. Field of the Invention
The present invention relates to an unsymmetrical dipole antenna, and more particularly, to an unsymmetrical dipole antenna for wideband or multi-frequency applications, capable of adjusting appearance while meeting a product structure.
2. Description of the Prior Art
Antennas are utilized for emitting or receiving radio waves, to transmit or exchange radio signals. An electronic product with wireless communication function, e.g. notebook computer, personal digital assistant, etc., generally utilizes a built-in antenna to access a wireless network. Therefore, to facilitate a user's access to the wireless communication network, an ideal antenna should maximize its bandwidth within a permitted range, while minimizing physical dimensions to accommodate the trend for smaller-sized portable wireless communication devices, and integrating the antennas into the portable wireless communication devices. Additionally, with the advance of wireless communication technology, operating frequencies of different wireless communication systems may be different. Therefore, the ideal antenna should be able to cover the required bands of different wireless communication networks via a single radiator.
In the prior art, one of common wireless communication antennas is planar inverted-F antenna (PIFA). As implied in the name, a shape of PIFA is similar to an inverted and rotated “F”. In general, a basic structure of PIFA includes a radiating element and a metal plane with a large area to form a “ground”, thereby wasting a lot of areas. Furthermore, PIFA radiating element requires a long length for a low frequency application (e.g. 800 MHz), causing large area and high cost, which is not suitable for a compact mobile device.
Therefore, it is a common goal in the industry to effectively increase the bandwidth of antennas, as well as meet the space constraints of the compact mobile devices.